Organic electroluminescent materials and devices

ABSTRACT

A compound is disclosed that has a metal coordination complex structure having at least two ligands coordinated to the metal; wherein the compound has a first substituent R 1  at one of the ligands&#39; periphery; wherein a first distance is defined as the distance between the metal and one of the atoms in R 1  where that atom is the farthest away from the metal among the atoms in R 1 ; wherein the first distance is also longer than any other atom-to-metal distance between the metal and any other atoms in the compound; and wherein when a sphere having a radius r is defined whose center is at the metal and the radius r is the smallest radius that will allow the sphere to enclose all atoms in the compound that are not part of R 1 , the first distance is longer than the radius r by at least 2.9 Δ.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 15/619,217, filed on Jun. 9, 2017, which claimspriority under 35 U.S.C. § 119(e)(1) from U.S. Provisional ApplicationSer. No. 62/352,119, filed Jun. 20, 2016, 62/516,329, filed Jun. 7,2017, 62/352,139, filed Jun. 20, 2016, 62/450,848, filed Jan. 26, 2017,62/479,795, filed Mar. 31, 2017, and 62/480,746, filed Apr. 3, 2017, theentire contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to compounds for use as phosphorescentemitters, and devices, such as organic light emitting diodes, includingthe same. More specifically, this disclosure relates to organometalliccomplexes having large aspect ratio in one direction and their use inOLEDs to enhance the efficiency.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting diodes/devices (OLEDs), organic phototransistors, organicphotovoltaic cells, and organic photodetectors. For OLEDs, the organicmaterials may have performance advantages over conventional materials.For example, the wavelength at which an organic emissive layer emitslight may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Alternatively the OLED can be designed to emit white light. Inconventional liquid crystal displays emission from a white backlight isfiltered using absorption filters to produce red, green and blueemission. The same technique can also be used with OLEDs. The white OLEDcan be either a single EML device or a stack structure. Color may bemeasured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY

According to an aspect of the present disclosure, a compound isdisclosed that has a metal coordination complex structure having atleast two ligands coordinated to the metal; wherein the compound has afirst substituent R¹ at one of the ligands' periphery; wherein a firstdistance is defined as the distance between the metal and one of theatoms in R¹ where that atom is the farthest away from the metal amongthe atoms in R¹; wherein the first distance is also longer than anyother atom-to-metal distance between the metal and any other atoms inthe compound; and wherein when a sphere having a radius r is definedwhose center is at the metal and the radius r is the smallest radiusthat will allow the sphere to enclose all atoms in the compound that arenot part of R¹, the first distance is longer than the radius r by atleast 2.9 Å.

According to another aspect, an OLED is disclosed that comprises: ananode; a cathode; and an organic layer, disposed between the anode andthe cathode, comprising a compound having a metal coordination complexstructure; wherein the compound is capable of functioning as an emitterin an organic light emitting device at room temperature; wherein thecompound has at least two ligands coordinated to the metal; wherein thecompound has a first substituent R¹ at one of the ligands' periphery;wherein a first distance is the distance between the metal and an atomin R¹ that is the farthest away from the metal; wherein the firstdistance is longer than any distance between the metal and any otheratoms in the compound; and wherein when a sphere having a radius r isdefined whose center is the metal and the radius r is the smallestradius that will allow the sphere to enclose all atoms in the compoundthat are not part of R¹, the first distance is longer than the radius rby at least 2.9 Å.

According to another aspect, an OLED is disclosed that comprises: ananode; a cathode; and an emissive layer, disposed between the anode andthe cathode, comprising a phosphorescent emitting compound; wherein thephosphorescent emitting compound has an intrinsic emission spectrum witha full width at half maximum (FWHM) value of no more than 40 nm; whereinthe OLED has an EQE of at least 25% measured at 0.1 mA/cm² at roomtemperature when a voltage is applied across the device.

According to another aspect, a consumer product comprising an OLED isdisclosed wherein the OLED comprises: an anode; a cathode; and anorganic layer, disposed between the anode and the cathode, comprising acompound having a metal coordination complex structure; wherein thecompound is capable of functioning as an emitter in an organic lightemitting device at room temperature; wherein the compound has at leasttwo ligands coordinated to the metal; wherein the compound has a firstsubstituent R¹ at one of the ligands' periphery; wherein a firstdistance is the distance between the metal and an atom in R¹ that is thefarthest away from the metal; wherein the first distance is longer thanany distance between the metal and any other atoms in the compound; andwherein when a sphere having a radius r is defined whose center is themetal and the radius r is the smallest radius that will allow the sphereto enclose all atoms in the compound that are not part of R¹, the firstdistance is longer than the radius r by at least 2.9 Å.

According to another aspect, a consumer product comprising an OLED isdisclosed wherein the OLED comprises: an anode; a cathode; and anemissive layer, disposed between the anode and the cathode, comprising aphosphorescent emitting compound; wherein the phosphorescent emittingcompound has an intrinsic emission spectrum with a FWHM value of no morethan 40 nm and an EQE of at least 25% measured at 0.1 mA/cm² at roomtemperature when a voltage is applied across the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows an example of 2-phenylpyridine based Iridium phosphorescentemitter.

FIG. 4 shows an example of 4-substituted pyridine structure where thetransition dipole moment vector (dashed line) is along the molecularlong axis.

FIG. 5 shows an example of phenylpyridine based ligand wheresubstitutions at R¹, R², R³, and R⁴ allows for long axis alignment withdashed TDM vector.

FIG. 6 shows diketone ligated structure wherein trans-nitrogen ligatedC—N ligands introduce C₂ rotational symmetry.

FIG. 7 shows a schematic illustration of trans-nitrogen axis and apreferred alignment of long axis and TDM vector with this axis.

FIG. 8 shows a schematic illustration of C₃ or pseudo-C₃ symmetricstructure and a preferred alignment of R¹, R², and R³ molecular longaxis as well as the TDM vector with this C₃ rotation plane.

FIG. 9 shows one of the possible ligand substitution patterns to enablemolecular long axis and TDM alignment with C₃ rotation plane offac-tris-bidentate organometallic emitter.

FIG. 10 shows an example bottom emission OLED device stack fordetermination of EQE in the absence of optical enhancement.

FIG. 11 shows the experimental setup for the angle dependentphotoluminescence experiment used to measure emitter alignment.

FIG. 12 shows an experimental data comparing horizontally orientedemitter Compound 152 with randomly (isotropically) oriented emittertris(2-phenylpyridine) iridium.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated byreference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJP. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. Such consumer products would include anykind of products that include one or more light source(s) and/or one ormore of some type of visual displays. Some examples of such consumerproducts include flat panel displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, laser printers, telephones,cell phones, tablets, phablets, personal digital assistants (PDAs),wearable devices, laptop computers, digital cameras, camcorders,viewfinders, micro-displays (displays that are less than 2 inchesdiagonal), 3-D displays, virtual reality or augmented reality displays,vehicles, video walls comprising multiple displays tiled together,theater or stadium screen, and a sign. Various control mechanisms may beused to control devices fabricated in accordance with the presentinvention, including passive matrix and active matrix. Many of thedevices are intended for use in a temperature range comfortable tohumans, such as 18 degrees C. to 30 degrees C., and more preferably atroom temperature (20-25 degrees C.), but could be used outside thistemperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The term “halo,” “halogen,” or “halide” as used herein includesfluorine, chlorine, bromine, and iodine.

The term “alkyl” as used herein contemplates both straight and branchedchain alkyl radicals. Preferred alkyl groups are those containing fromone to fifteen carbon atoms and includes methyl, ethyl, propyl,1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl,1,2-dimethylpropyl, 2,2-dimethylpropyl, and the like. Additionally, thealkyl group may be optionally substituted.

The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals.Preferred cycloalkyl groups are those containing 3 to 10 ring carbonatoms and includes cyclopropyl, cyclopentyl, cyclohexyl, adamantyl, andthe like. Additionally, the cycloalkyl group may be optionallysubstituted.

The term “alkenyl” as used herein contemplates both straight andbranched chain alkene radicals. Preferred alkenyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkenyl groupmay be optionally substituted.

The term “alkynyl” as used herein contemplates both straight andbranched chain alkyne radicals. Preferred alkynyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkynyl groupmay be optionally substituted.

The terms “aralkyl” or “arylalkyl” as used herein are usedinterchangeably and contemplate an alkyl group that has as a substituentan aromatic group. Additionally, the aralkyl group may be optionallysubstituted.

The term “heterocyclic group” as used herein contemplates aromatic andnon-aromatic cyclic radicals. Hetero-aromatic cyclic radicals also meansheteroaryl. Preferred hetero-non-aromatic cyclic groups are thosecontaining 3 to 7 ring atoms which includes at least one hetero atom,and includes cyclic amines such as morpholino, piperidino, pyrrolidino,and the like, and cyclic ethers, such as tetrahydrofuran,tetrahydropyran, and the like. Additionally, the heterocyclic group maybe optionally substituted.

The term “aryl” or “aromatic group” as used herein contemplatessingle-ring groups and polycyclic ring systems. The polycyclic rings mayhave two or more rings in which two carbons are common to two adjoiningrings (the rings are “fused”) wherein at least one of the rings isaromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl,heterocycles, and/or heteroaryls. Preferred aryl groups are thosecontaining six to thirty carbon atoms, preferably six to twenty carbonatoms, more preferably six to twelve carbon atoms. Especially preferredis an aryl group having six carbons, ten carbons or twelve carbons.Suitable aryl groups include phenyl, biphenyl, triphenyl, triphenylene,tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, and azulene, preferably phenyl,biphenyl, triphenyl, triphenylene, fluorene, and naphthalene.Additionally, the aryl group may be optionally substituted.

The term “heteroaryl” as used herein contemplates single-ringhetero-aromatic groups that may include from one to five heteroatoms.The term heteroaryl also includes polycyclic hetero-aromatic systemshaving two or more rings in which two atoms are common to two adjoiningrings (the rings are “fused”) wherein at least one of the rings is aheteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls,aryl, heterocycles, and/or heteroaryls. Preferred heteroaryl groups arethose containing three to thirty carbon atoms, preferably three totwenty carbon atoms, more preferably three to twelve carbon atoms.Suitable heteroaryl groups include dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine, preferablydibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole,indolocarbazole, imidazole, pyridine, triazine, benzimidazole,1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogsthereof. Additionally, the heteroaryl group may be optionallysubstituted.

The alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic group,aryl, and heteroaryl may be unsubstituted or may be substituted with oneor more substituents selected from the group consisting of deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether,ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

As used herein, “substituted” indicates that a substituent other than His bonded to the relevant position, such as carbon. Thus, for example,where R¹ is mono-substituted, then one R¹ must be other than H.Similarly, where R¹ is di-substituted, then two of R¹ must be other thanH. Similarly, where R¹ is unsubstituted, R¹ is hydrogen for allavailable positions.

The “aza” designation in the fragments described herein, i.e.aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more ofthe C—H groups in the respective fragment can be replaced by a nitrogenatom, for example, and without any limitation, azatriphenyleneencompasses both dibenzo[fh]quinoxaline and dibenzo[fh]quinoline. One ofordinary skill in the art can readily envision other nitrogen analogs ofthe aza-derivatives described above, and all such analogs are intendedto be encompassed by the terms as set forth herein.

It is to be understood that when a molecular fragment is described asbeing a substituent or otherwise attached to another moiety, its namemay be written as if it were a fragment (e.g. phenyl, phenylene,naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g.benzene, naphthalene, dibenzofuran). As used herein, these differentways of designating a substituent or attached fragment are considered tobe equivalent.

In the present disclosure, we describe a method for achieving emittertransition dipole alignment for improvement of OLED device performance.Increasing the horizontal alignment of the transition dipole momentvector responsible for photon emission within individual emitter leadsto an increased outcoupling, and thus increased efficiency. Increasingmolecular aspect ratio of the emitter, through increased linearity orplanarity, allows for non-isotropic orientation of the emitter in theOLED EML. Correlation of the transition dipole moment with this linearlong axis or plane allows for the emitter orientation to translate totransition dipole orientation and improved light outcoupling. Thesechanges can improve light outcoupling and device efficiency by up to 50%versus a randomly oriented emitter.

Alignment of Emissive Transition Dipole Moment:

The method described herein improves OLED performance by maximizinglight outcoupling through molecular alignment. Despite very high excitonconversion efficiencies and emission quantum yields achieved throughphosphorescent OLED materials, device efficiency is ultimately limitedby light extraction efficiency. Extraction of photons emitted from theemissive layer (EML) of an OLED stack depends greatly on the directionof the photon emission. Photons propagating normal to the devicesubstrate have a high probability of extraction, whereas those photonspropagating at a high angle with respect to the substrate's orthogonaldirection stand a much greater chance of being lost and not be extracteddue to internal reflection, waveguided modes and coupling to surfaceplasmon modes.

In an individual emitter compound, light emission occurs perpendicularto the triplet to ground state transition dipole moment (TDM). As such,increasing the number of emitter compound molecules whose TDM vector ishorizontally aligned with respect to the OLED's substrate results in ahigher light extraction efficiency, and thus higher device efficiency(external quantum efficiency—EQE). This horizontal orientation factorcan be described statistically in an ensemble of emitter molecules bythe ratio θ of the horizontal component of the TDM vector, TDM_(∥), tothe sum of the vertical component, TDM_(⊥), and the horizontalcomponent. In other words: θ=TDM_(∥)/(TDM_(⊥)+TDM_(∥)). The ratio θ willbe hereinafter referred to as the horizontal dipole ratio (“HDR”).

The horizontal dipole ratio θ may be measured by angle dependentphotoluminescence measurements. By comparing the measured emissionpattern of a photoexcited thin film sample, as a function ofpolarization, to the computationally modeled pattern, one can determinethe TDM vector's orientation for a given sample. The horizontal dipoleratio θ has a very significant effect on resulting device efficiency. Ina typical bottom emission device structure (as shown in FIG. 10) with nomicrocavity or other optical enhancement and material refractive indices1.5-2.0, a randomly oriented emitter (θ=0.67) can achieve a maximumdevice EQE of roughly 28% assuming quantitative emission and chargerecombination efficiency (achievable at very low current density <1mA/cm²). In the case of a perfectly horizontal emitter, with θ=1, EQE inexcess of 40% is achievable in an OLED device with a PLQY of 100% andcharge recombination efficiency of 100%.

In general, increased emission outcoupling depends on two primaryfactors: (1) triplet to ground state TDM vector alignment within anemitter compound molecule and (2) molecular alignment of the emitterwithin an EML structure. As such, it is necessary to control bothfactors in unison to effectively achieve alignment of the TDM vector toenhance the OLED performance. Furthermore, both factors may not bediscrete, but a distribution of alignments. Near-degenerate emissiveoptical transitions may result in a distribution of differentiallyoriented TDM vectors that is described by Boltzmann statistics.Structurally, molecular alignment of the emitter in an amorphous EMLmedium results in a distribution of emitter alignments which may varythroughout the EML layer. As such, enhancement of device performance maybe realized through both preferential emission from a single opticaltransition and strong alignment of this transition within a device EML.

Single TDM Vector Molecular Alignment:

In order to realize an aligned TDM vector within the device,preferential emitter alignment must be instilled into the host andemitter materials. This is achieved, primarily, through a high aspectratio emitter molecule. It is found that high aspect ratio rod-like ordisk-like structures may be preferentially oriented in a nominallyamorphous film prepared by methods such as thermal vapor deposition,spin coating, ink jet printing, and organic vapor jet printing.

In emitters with a single preferential emissive transition, a rod-likestructure can be chosen to optimize alignment with the TDM vector whilestill minimizing molecular weight. In emitters similar in structure totris(2-phenylpyridine) iridiumn (Ir(ppy)₃, FIG. 3), this is achievedthrough creation of a long molecular axis extending though the iridiummetal center. The directionality of the long molecular axis may dependon orientation of the TDM vector, as discussed below.

Referring to FIG. 4, in the case of emitters in which the TDM vector isroughly aligned with the iridium-nitrogen bond (depicted with dashedarrow), the molecular long axis may be created through an appropriatesubstitution at the pyridine 4-position (R¹ in FIG. 4). For example,aryl, heteroaryl, alkyl, or cycloalkyl substituents may be introduced atthis position to facilitate the formation of a high aspect ratiorod-like structure in which the molecular long axis passes roughlythrough the iridium-nitrogen bond and through this substituent group. Weaim to align the TDM vector axis with this high aspect ratio molecularlong axis with an angle between these two axes preferably less than 30°,more preferably less than 10°. A preferred length of the substituent,R¹, ranges from 3 to 15 Å, more preferably from 4 to 9 Å. We predictthat applying this molecular design with judicious choice ofsubstituents can result in HDR of up to 0.85 and a resulting large EQEincrease.

Similarly, a rod-like structure may be used in emitters containing asingle preferential TDM vector roughly bisecting the bidentate emittingligand (see FIG. 5, depicted in dashed line). In this case, elongationby aryl, heteroaryl, alkyl, or cycloalkyl substitution at the pyridine3- and 4-position in conjunction with substitution at the phenyl 5- and6-positions may be used to generate a molecular long axis roughlybisecting the bidentate emitting ligand. For example, alkyl substitutionat the pyridine 4-position and fused heteroaryl substitution at thephenyl 5- and 6-positions results in net elongation in the TDM vectordirection. Similarly, twisted aryl substitution at the phenyl 6-positionresults in a more rod like elongation in this TDM vector axis. We aim toalign the TDM vector axis with this high aspect ratio molecular longaxis with an angle between these two axes preferably less than 300, morepreferably less than 10°. The preferred length of the substituent, R¹/R²and R³/R⁴, ranges from 3 to 15 Å, more preferably from 4 to 9 Å. Becausethis substitution pattern may introduce a larger planar system to alignwith the EML surface, we predict further enhanced HDR of up to 0.9.

Ligand Energy Gap:

For homoleptic Iridium emitters, wherein all three bidentate ligands areidentical, degeneracy of the three optical transitions leads to arandomization of the transition dipole orientation. As is the case withhomoleptic emitters, heteroleptic emitters may also have emissiondistributed between degenerate or near-degenerate transitions. Thesetransitions may be centered on different ligands and thus have largelyorthogonal TDM vectors. This results in an overall scrambling of anyemission alignment that may be afforded from molecular alignment.

We note that the very small energy gap between nearly identicalphenylpyridine based ligands results in largely isotropic emission inIr(ppy)₃-type emitters, even in strongly oriented rod-like structures.In these cases, Boltzmann statistics largely describe the probability ofemission from near-degenerate transitions. As such, we find that thelocalization of the emissive transition is highly sensitive to theenergy gap between the various transitions in question. In order tostrongly localize emission and improve TDM alignment, the preferredenergy gap between emission centered on the emissive ligand versus theancillary ligand(s) is above 0.05 eV and more preferably 0.10 eV.

Furthermore, any preferential alignment induced by a long axispositioned along one of the ligands not primarily responsible for theemissive transition may result in a low horizontal dipole ratio, θ. Thiscase, where the one of the aforementioned alignment motifs is applied onone of the emitter ancillary ligands, is to be avoided as this mayresult in HDR values below 0.67 (isotropic orientation).

Symmetry and Geometry of TDM Vectors:

In cases where large energy gaps may not be afforded by energetic tuningof emissive and ancillary ligand structures, as is the case with manyhigh energy blue and green emitters, symmetry and molecular geometry maybe used to produce highly aligned emission from multiple ligands. Wenote the largely orthogonal nature of the degenerate TDM vectors ofIr(ppy)₃ and the perfectly parallel nature of those in diketone ligatedred emitters with symmetric emitting ligands. In the case of degenerateemission, these perpendicular and parallel relationships give rise tonegation and enhancement, respectively, of any aligned emission due tomolecular alignment in the EML.

In these diketone ligated Iridium emitters, a preferentialtrans-orientation of the Iridium-nitrogen bond results in a C₂ axis ofsymmetry in the structure. See FIG. 6. We propose using this C₂ axis toenhance alignment induced by elongation of the TDM vector axis. See FIG.7. If the non-ketone ligand is designed to have both (1) TDM vector and(2) steric long axis aligned with the Ir—N bond, the C₂ symmetryenhances alignment due to the parallel TDM vectors on the two emissiveligands. This allows for very high HDR values in excess of 0.85.

Regarding tris substituted compounds, wherein the emission has an equalor near-equal probability of being centered on each of the threeligands, it is preferable to align both: (1) the TDM vector and (2) thelong axis with the plane containing the compounds three-fold rotationalsymmetry. In these homolepticfac compounds, this C₃ plane roughlybisects the angle between the two metal ligand bonds of each bidentateligand. See FIG. 8. As such, the TDM vector of these complexes should beroughly bisecting this angle, preferably making less than a 20° anglebetween the C₃ plane and the TDM vector and more preferably less than10°.

The resulting planar or nearly-planar arrangement of the three TDMvectors can then contribute to efficiency gains if changes in the aspectratio induce preferential horizontal alignment of this plane.Lengthening each ligand along this C₃ plane results in a very planarstructure with a high aspect ratio. One such structure is shown in FIG.9 where R is alkyl, cycloalkyl, aryl, or heteroaryl. Same R can also beat the similar position on the pyridine ring. The molecular aspect ratiois dictated by this radius between the metal center and the terminus ofthe R-group which is preferably longer than 4 Å and more preferablylonger than 8 Å. Furthermore, it is preferable to have this vectorbetween metal center and R-group terminus in the C₃ plane with an anglebetween the vector and plane less than 20° and more preferably less than10°.

Emitters containing two identical emitting ligands or, more generally,two ligands primarily responsible for emission may be developed suchthat their long axes and TDM vectors are non-orthogonal. With respect toeach ligand individually, the long axis and TDM vector may be collinear,as described above. When this long axis of one ligand is at a largeangle (q) with respect to that of the second emitting ligand,enhancement of device efficiency may be observed. In this case, becausethe emitter molecular alignment can be described by a distribution oforientations in the amorphous EML, a bent shape where 90°<φ<180° resultsin a device efficiency enhancement by virtue of both TDM vectors beingroughly aligned with the long axis formed between the two ligands. Thisis achieved where the TDM vector is preferably bisecting the bidentateligand and also slightly out of the ligand plane. We propose using twodegenerate or near-degenerate emissive ligands with thispseudo-symmetric orientation of TDM vectors to induce HDR values inexcess of 0.7 and, more preferably, 0.8.

Host Induced Dopant Alignment:

Because the alignment of an emitter within the EML originates from thedifferential interaction of the emitter with the EML material and thedepositing medium (vacuum, air, inert gas, solvent, etc.), it isexpected that the interaction between the host and emitter materials hasan effect on the resulting orientation of the emitter TDM vector. Justas electrostatic interactions drive high aspect ratio emitter moleculesto lie flat in the EML structure, other strong host-emitter interactionsmay be used to drive alignment. These interactions may includepi-stacking, hydrogen bonding, use of functional groups with a stronginteraction (including polar, non-polar, fluorinated, or alkyl groupswhich may interact between host/dopant or drive intercalation orsegregation effects), donor-acceptor pi-interactions driven byinteractions between electron rich and electron poor aromatic moieties.

Optimizing emitter-host interactions to induce dopant alignment may alsodepend strongly on planarity of the dopant and/or host molecules.Especially in the case where strong pi-stacking interactions lead toalignment, increased planarity of these molecules is expected to resultin a stronger interaction and thus a higher degree of alignment. In thiscase, it is preferential to increase overall planarity of the dopantthrough judiciously introducing dihedral twisting of pi-planes toincrease the number of co-aligned aromatic cycles in the molecule. Itmay also be desirable to increase the planarity of the host moleculethrough similar strategies as well as increasing conjugation length,increase charge transfer character in the host, and intra- andinter-molecular hydrogen bonding. These differences in host inducedemitter alignment may be measured directly through photoluminescencetechniques in emitter:host samples relative to emitter:mCP (where mCP is1,3-Bis(N-carbazolyl)benzene, a disordered and non-orienting host).

To the extent that underlying layers of the device stack affect thealignment of the host or dopant material near the interface, it may alsobe preferred to introduce these aligning or templating motifs to theelectron blocking layer (EBL) or other underlying layers.

According to an aspect of the present disclosure, a compound isdisclosed that has a metal coordination complex structure and thecompound is capable of functioning as an emitter in an OLED at roomtemperature. For the purposes of this description, room temperaturerefers to a temperature range of 20-25° C. The compound has at least twoligands coordinated to the metal; wherein the compound has a firstsubstituent R¹ at one of the ligands' periphery; wherein a firstdistance is defined as the distance between the metal and one of theatoms in R¹ where that atom is the farthest away from the metal amongthe atoms in R¹; wherein the first distance is also longer than anyother atom-to-metal distance between the metal and any other atoms inthe compound; and wherein when a sphere having a radius r is definedwhose center is at the metal and the radius r is the smallest radiusthat will allow the sphere to enclose all atoms in the compound that arenot part of R¹, the first distance is longer than the radius r by atleast 2.9 Å. 2.9 Å represents the diameter of a phenyl ring. It shouldbe noted that the sphere as defined above does not exclude any of theatoms in R¹ from being enclosed in the sphere. As used herein, beingenclosed in the sphere means that the atom is located at a distance thatis less than or equal to the radius r from the metal.

In some embodiments of the compound, the first distance is longer thanthe radius r by at least 4.3 Å. In some embodiments of the compound, thefirst distance is longer than the radius r by at least 7.3 Å.

In some embodiments of the compound, the compound further has a secondsubstituent R² at one of the ligands' periphery; wherein a seconddistance is defined as the distance between the metal and one of theatoms in R² where that atom is the farthest away from the metal amongthe atoms in R²; and wherein when the radius r is the smallest radiusthat will allow the sphere to enclose all atoms in the compound that arenot part of R¹ or R², the second distance is longer than r by at least1.5 Å.

In some embodiments of the compound that has the second substituent R²,R¹ and R² are on different ligands. In some embodiments of the compound,the second distance is longer than r by at least 2.9 Å. In someembodiments, the second distance is longer than r by at least 4.3 Å. Insome embodiments, the second distance is longer than r by at least 7.3Å. In some embodiments, the first and second distances are all longerthan r by at least 4.3 Å. In some embodiments, the first and seconddistances are all longer than r by at least 7.3 Å.

In some embodiments of the compound that has the second substituent R²,R¹ is attached to an aromatic ring having a first coordination atom, R²is attached to an aromatic ring having a second coordination atom; andwherein the first coordination atom is in a trans configuration to thesecond coordination atom relative to the metal.

In some embodiments of the compound, the compound further has a thirdsubstituent R³ at one of the ligands' periphery; wherein a thirddistance is defined as the distance between the metal and one of theatoms in R³ where that atom is the farthest away from the metal amongthe atoms in R³; and wherein when the radius r is the smallest radiusthat will allow the sphere to enclose all atoms in the compound that arenot part of R¹, R², or R³, the third distance is longer than r by atleast 1.5 Å.

In some embodiments of the compound that has the third substituent R³,the substituents R¹, R², and R³ are on different ligands. In someembodiments of the compound, the third distance is longer than r by atleast 2.9 Å. In some embodiments, the third distance is longer than r byat least 4.3 Å. In some embodiments, the third distance is longer than rby at least 7.3 Å.

The following Table 1 lists the maximum linear length for varioussubstituent groups defined along their long axis. This maximum linearlength is defined as the distance between the two atoms that are thefarthest apart along the long axis of the particular substituent group.The listed values can be used to estimate how much a given substituentat one of the ligands' periphery in a coordination complex would extendbeyond the radius r of the sphere that would enclose all atoms in thecoordination complex that are not part of that particular substituent.For example, in an embodiment of the coordination complex that only hasthe first substituent R¹, the difference between the first distance andthe radius r can be estimated using the Table 1 depending on theparticular chemical group involved in the first substituent R¹. If anembodiment of the coordination complex has additional substituents suchas the second and third substituents R² and R³ at the periphery of oneor more of the ligands in the complex, the Table 1 can be used toestimate the difference between the second or the third distances andthe radius r by considering the particular substituent groups involvedin the substituents R² or R³. The following Table 1 can be used tocalculate the difference between two substituents. For example, if firstsubstituent is phenyl, the second substituent is tolyl, then the secondsubstituent is longer than first substituent by one C—C bond, which is1.5 Å. In another example, if the second substituent is biphenyl, thenthe second substituent is longer than the first substituent by C—C₆H₅,which is 4.3 Å. Any two or more of the following fragments can be linkedtogether, and its distance can be calculated by simply adding up thesenumbers plus the total length of the single C—C bond distance used toconnect them.

TABLE 1 The difference in bond length between the The difference betweentwo substituent two substituents. (Å) C—C  1.5

 2.9

 3.0

 4.3

 4.4

 5.2

 5.9

 7.3

 8.8

10.3 two C—C  3.0

 7.3

 8.8

13.1

17.6

19.1

In some embodiments of the compound that has the third substituent R³,the first, second, and third distances are all longer than r by at least4.3 Å. In some embodiments, the first, second, and third distances areall longer than r by at least 7.3 Å. In some embodiments, the first,second, and third distances are each independently longer than r by atleast one of the distances listed in the Table 1. In some furtherembodiments, the first, second, and third distances are all longer thanr by at least one of the distances listed in the Table 1.

In some embodiments of the compound that has the third substituent R³,the compound has an octahedral coordination geometry with threebidentate ligands, wherein each of the three bidentate ligands havingtwo coordination atoms and a midpoint defined between the twocoordination atoms; wherein the three midpoints define a first plane;and wherein each atom in R¹, R², and R³ have a point-to-plane distanceless than 5 Å relative to the first plane. A “point-to-plane” distancerefers to the shortest distance between a plane and a point that is notin the plane.

In some embodiments of the compound having R³, any atom in R¹, R², andR³ has a point-to-plane distance less than 4 Å relative to the firstplane. In some embodiments, any atom in R¹, R², and R³ has apoint-to-plane distance less than r relative to the first plane.

In some embodiments of the compound, the compound has a transitiondipole moment axis; and wherein an angle between the transition dipolemoment axis and an axis along the first distance for R¹, is less than40°. A “transition dipole moment axis” is an axis along the transitiondipole moment. In some embodiments, the angle between the transitiondipole moment axis and an axis along the first distance is less than30°. In some embodiments, the angle between the transition dipole momentaxis and an axis along the first distance is less than 20°. In someembodiments, the angle between the transition dipole moment axis and anaxis along the first distance is less than 150. In some embodiments, theangle between the transition dipole moment axis and an axis along thefirst distance is less than 10°. In some embodiments, the angle betweenthe transition dipole moment axis and an axis along the first distanceis less than 35°. In some embodiments, the angle between the transitiondipole moment axis and an axis along the first distance is less than25°. In some embodiments, the angle between the transition dipole momentaxis and an axis along the first distance is less than 5°.

In some embodiments of the compound where the first distance for R¹ issignificantly longer than the second distance for R² and the thirddistance for R³ or there is no R² or R³, the free energy differencebetween emission centered on the three different ligands is considered.In order to compare the free energy of the ligand having R¹, a firsthomoleptic metal complex formed of ligands that are same as the ligandhaving R¹ will have a triplet energy that is lower than the tripletenergy of a second homoleptic metal complex that is formed of ligandsthat are any of the other ligands in the compound, by at least 0.02 eV.In other embodiments, the triplet energy of the first homoleptic metalcomplex is lower than the triplet energy of the second homoleptic metalcomplex by at least 0.05 eV. In other embodiments, the triplet energy ofthe first homoleptic metal complex is lower than the triplet energy ofthe second homoleptic metal complex by at least 0.1 eV. In otherembodiments, the triplet energy of the first homoleptic metal complex islower than the triplet energy of the second homoleptic metal complex byat least 0.15 eV.

In some embodiments of the compound, the substituents R¹, R², and R³ areeach independently selected from the group consisting of:

In some embodiments of the compound, the compound is capable offunctioning as a phosphorescent emitter, a fluorescent emitter, or adelayed fluorescent emitter in an organic light emitting device at roomtemperature.

In some embodiments of the compound, the compound is capable of emittinglight from a triplet excited state to a ground singlet state at roomtemperature.

In some embodiments of the compound, the compound has a metal-carbonbond.

In some embodiments of the compound, the metal is selected from thegroup consisting of Ir, Rh, Re, Ru, Os, Pt, Pd, Au, Ag, and Cu. In someembodiments, the metal is Ir. In some embodiments, the metal is Pt.

In some embodiments of the compound, the compound has a neutral charge.

In some embodiments of the compound, each ligand in the compound isdifferent from each other.

In some embodiments of the compound, the compound has an octahedralcoordination geometry formed by three bidentate ligands, two tridentateligands, one tetradentate and one bidentate ligands, or one hexadentateligand.

In some embodiments of the compound, the compound has a tetrahedralcoordination geometry formed by two bidentate ligands, or onetetradentate ligand.

In some embodiments of the compound, the compound comprises a firstbenzene ring coordinated to the metal; and wherein the first benzenering is fused by a second aromatic ring. In some embodiments, the secondaromatic ring is fused by a third aromatic ring. In some embodiments,the third aromatic ring is fused by a fourth aromatic ring.

In some embodiments of the compound, wherein the compound has theformula of M(L¹)_(x)(L²)_(y)(L³)_(z);

wherein L¹, L², and L³ can be the same or different;

wherein x is 1, 2, or 3;

wherein y is 0, 1, or 2;

wherein z is 0, 1, or 2;

wherein x+y+z is the oxidation state of the metal M;

wherein L¹, L², and L³ are each independently selected from the groupconsisting of:

wherein each X¹ to X¹⁷ are independently selected from the groupconsisting of carbon and nitrogen;

wherein Z¹, Z², and Z³ are each independently a carbon or nitrogen;

wherein X is selected from the group consisting of BR′, NR′, PR′, O, S,Se, C═O, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″;

wherein R′ and R″ are optionally fused or joined to form a ring;

wherein each R_(a), R_(b), R_(c), and R_(d) may represent from monosubstitution to the possible maximum number of substitution, or nosubstitution;

wherein R′, R″, R_(a), R_(b), R_(c), R_(d), R_(e) are each independentlyselected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof; and

wherein any two R_(a), R_(b), R_(c), and R_(d) are optionally fused orjoined to form a ring or form a multidentate ligand; and

wherein at least one of the R_(a), R_(b), R_(c), and R_(d) includes R¹.

In some embodiments of the compound having the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), at least one pair of substituents R_(a),R_(b), R_(c), and R_(d) within the same ring are joined and fused into aring.

In some embodiments of the compound having the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), at least one pair of substituents R_(a),R_(b), R_(c), and R_(d) between two nearby rings are joined and fusedinto a ring.

In some embodiments of the compound having the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula of Ir(L¹)₂(L²).

In some embodiments of the compound having the formula of Ir(L)₂(L²), L¹has the formula selected from the group consisting of:

and

wherein L² has the formula:

In some embodiments, L² has the formula:

wherein R_(e), R_(f), R_(h), and R₁ are independently selected fromgroup consisting of alkyl, cycloalkyl, aryl, and heteroaryl;

wherein at least one of R_(e), R_(f), R_(h), and R₁ has at least twocarbon atoms; and

wherein R_(g) is selected from group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile,sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In some embodiments of the compound having the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula selected fromthe group consisting of Ir(L¹)(L²)(L³), Ir(L¹)₂(L²), and Ir(L¹)³;

wherein L¹, L², and L³ are different and each independently selectedfrom the group consisting of:

In some embodiments of the compound having the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula of Pt(L¹)₂ orPt(L¹)(L²). In some embodiments, L¹ is connected to the other L¹ or L²to form a tetradentate ligand.

In some embodiments of the compound having the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula of M(L¹)₂ orM(L¹)(L²); wherein M is Ir, Rh, Re, Ru, or Os; and wherein L¹ and L² areeach a different tridentate ligand.

In some embodiments of the compound, the compound is selected from thegroup consisting of:

According to another aspect of the present disclosure, an OLED isdisclosed. The OLED comprising: an anode; a cathode; and

an organic layer, disposed between the anode and the cathode, comprisinga compound having a metal coordination complex structure;

wherein the compound is capable of functioning as an emitter in anorganic light emitting device at room temperature;

wherein the compound has at least two ligands coordinated to the metal;

wherein the compound has a first substituent R¹ at one of the ligands'periphery;

wherein a first distance is the distance between the metal and an atomin R¹ that is the farthest away from the metal;

wherein the first distance is longer than any distance between the metaland any other atoms in the compound; and

wherein when a sphere having a radius r is defined whose center is themetal and the radius r is the smallest radius that will allow the sphereto enclose all atoms in the compound that are not part of R¹, the firstdistance is longer than the radius r by at least 2.9 Å.

In some embodiments of the OLED, the organic layer is an emissive layerand the compound having a metal coordination complex structure is anemissive dopant or a non-emissive dopant.

In some embodiments of the OLED where the organic layer furthercomprises a host, the host comprises a triphenylene containingbenzo-fused thiophene or benzo-fused furan;

wherein any substituent in the host is an unfused substituentindependently selected from the group consisting of C_(n)H_(2n+1),OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂),CH═CH—C_(n)H_(2n+1), C≡CC_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, andC_(n)H_(2n)—Ar₁, or the host has no substitution;

wherein n is from 1 to 10; and

wherein Ar_(n) and Ar₂ are independently selected from the groupconsisting of benzene, biphenyl, naphthalene, triphenylene, carbazole,and heteroaromatic analogs thereof.

In some embodiments of the OLED where the organic layer furthercomprises a host, the host comprises at least one chemical groupselected from the group consisting of triphenylene, carbazole,dibenzothiophene, dibenzofuran, dibenzoselenophene, azatriphenylene,azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, andaza-dibenzoselenophene.

In some embodiments of the OLED where the organic layer furthercomprises a host, the host is selected from the group consisting of:

and combinations thereof.

In some embodiments of the OLED where the organic layer furthercomprises a host, the host comprises a metal complex.

In some embodiments of the OLED, the compound having a metalcoordination complex structure has a HDR of at least 0.7. In someembodiments of the OLED, the compound having a metal coordinationcomplex structure has a HDR of at least 0.75. In some embodiments of theOLED, the compound having a metal coordination complex structure has aHDR of at least 0.8. In some embodiments of the OLED, the HDR of thecompound having a metal coordination complex structure is at least 0.85.In some embodiments of the OLED, the HDR of the compound having a metalcoordination complex structure is at least 0.9. In some embodiments ofthe OLED, the HDR of the compound having a metal coordination complexstructure is at least 0.95.

In some embodiments of the OLED, the organic layer further comprises ahost; and the compound has a HDR that is higher by at least 5% whencompared to the exact same device with mCP(1,3-bis(N-carbazolyl)benzene) as the host. In some embodiments of theOLED, the compound has a HDR that is higher by at least 10% compared tothe exact same device with mCP as host. In some embodiments of the OLED,the compound has a HDR that is higher by at least 20% when compared tothe exact same device with mCP as the host. In some embodiments of theOLED, the compound has a HDR that is higher by at least 30% whencompared to the exact same device with mCP as the host. In someembodiments of the OLED, the compound has a HDR that is higher by atleast 40% when compared to the exact same device with mCP as the host.

According to another aspect of the present disclosure, an OLED isdisclosed which comprises: an anode; a cathode; and an emissive layer,disposed between the anode and the cathode, comprising a phosphorescentemitting compound; wherein the phosphorescent emitting compound has anintrinsic emission spectrum with a FWHM value of no more than 45 nm, andthe OLED has an EQE of at least 25% at 0.1 mA/cm² at room temperaturewhen a voltage is applied across the device. In some embodiments, theFWHM value of the phosphorescent emitting compound's intrinsic emissionspectrum is no more than 43 nm. In some embodiments, the FWHM value ofthe phosphorescent emitting compound's intrinsic emission spectrum is nomore than 41 nm. In some embodiments, the FWHM value of thephosphorescent emitting compound's intrinsic emission spectrum is nomore than 39 nm. In some embodiments, the FWHM value of thephosphorescent emitting compound's intrinsic emission spectrum is nomore than 37 nm. In some embodiments, the FWHM value of thephosphorescent emitting compound's intrinsic emission spectrum is nomore than 35 nm. In some embodiments, the FWHM value of thephosphorescent emitting compound's intrinsic emission spectrum is nomore than 33 nm. In some embodiments, the FWHM value of thephosphorescent emitting compound's intrinsic emission spectrum is nomore than 31 nm. In some embodiments, the FWHM value of thephosphorescent emitting compound's intrinsic emission spectrum is nomore than 29 nm. In some embodiments, the FWHM value of thephosphorescent emitting compound's intrinsic emission spectrum is nomore than 27 nm. In some embodiments, the OLED has an EQE of at least27%. In some embodiments, the OLED has an EQE of at least 29%. In someembodiments, the OLED has an EQE of at least 31%. In some embodiments,the device lifetime to 95% luminance is 8 hours for a 400 nm≤λ_(max)≤500nm emitter, as measured at 20 mA/cm², 30 hours for a 500 nm≤λ_(max)≤590nm emitter as measured at 80 mA/cm², and 150 hours for a 590nm≤λ_(max)≤750 nm emitter, as measured at 80 mA/cm². In someembodiments, the device lifetime to 95% luminance is 12 hours for a 400nm≤λ_(max)≤500 nm emitter, as measured at 20 mA/cm², 45 hours for a 500nm≤λ_(max)≤590 nm emitter as measured at 80 mA/cm², and 225 hours for a590 nm≤λ_(max)≤750 nm emitter, as measured at 80 mA/cm². In someembodiments, the device lifetime to 95% luminance is 16 hours for a 400nm≤λ_(max)≤500 nm emitter, as measured at 20 mA/cm², 60 hours for a 500nm≤λ_(max)≤590 nm emitter as measured at 80 mA/cm², and 300 hours for a590 nm≤λ_(max)≤750 nm emitter, as measured at 80 mA/cm². In someembodiments, the device lifetime to 95% luminance is 20 hours for a 400nm≤λ_(max)≤500 nm emitter, as measured at 20 mA/cm², 75 hours for a 500nm≤λ_(max)≤590 nm emitter as measured at 80 mA/cm², and 375 hours for a590 nm≤λ_(max)≤750 nm emitter, as measured at 80 mA/cm².

The intrinsic emission spectrum of a phosphorescent emitting compound isdefined as the photoluminescence spectrum of a thermally evaporated<1-10% doped thin film of the emitter in the same host material used inthe OLED stack. As one of ordinary skill in the art would recognize, thedoping percentage should be limited to a regime that minimizesaggregation quenching and broadening. It is worth noting that thisemission spectrum may exhibit slight broadening or narrowing in an OLEDdue to optical and chemical factors.

It was found that the photoluminescence full width at half maximum(FWHM) of emitters was significantly decreased due to benzoannulation onan existing ring of the ligands. The photoluminescence spectralnarrowing of emitters will improve device performance such as EQE. Forexample, when the following Compound A (FWHM: 65 nm in solution) wasfused with an extra benzene ring, the benzoannulated Compound B has aFWHM of 19 nm, which is significantly narrower than Compound A. Likewisein solid state PMMA thin film, Compound B has a FWHM of 21 nm, which is47 nm narrower than Compound A in 5% doped PMMA solid film (FWHM:68 nm).

In some embodiments of the OLED, the phosphorescent emitting compound isa metal coordination complex, wherein the metal is selected from thegroup consisting of Ir, Rh, Re, Ru, Os, Pt, Pd, Au, Ag, and Cu. In someembodiments, the metal is Ir. In some embodiments, the metal is Pt.

In some embodiments of the OLED where the phosphorescent emittingcompound is a metal coordination complex, the phosphorescent emittingcompound is a benzene ring coordinated to the metal; wherein the benzenering is fused by a second aromatic ring. In some embodiments, the secondaromatic ring is fused by a third aromatic ring. In some embodiments,the third aromatic ring is fused by a fourth aromatic ring.

In some embodiments of the OLED where the phosphorescent emittingcompound in the OLED has an intrinsic emission spectrum with a FWHMvalue of no more than 45 nm and an EQE of at least 25% measured at 0.1mA/cm² at room temperature when a voltage is applied across the device,the phosphorescent emitting compound has a HDR of at least 0.7. In someembodiments of the OLED, the phosphorescent emitting compound has a HDRof at least 0.75. In some embodiments of the OLED, the phosphorescentemitting compound has a HDR of at least 0.8. In some embodiments of theOLED, the phosphorescent emitting compound has a HDR of at least 0.85.In some embodiments of the OLED, the phosphorescent emitting compoundhas a HDR of at least 0.9. In some embodiments of the OLED, thephosphorescent emitting compound has a HDR of at least 0.95.

In some embodiments of the OLED where the phosphorescent emittingcompound in the OLED has an intrinsic emission spectrum with a FWHMvalue of no more than 45 nm and an EQE of at least 25% at roomtemperature when a voltage is applied across the device, the emissivelayer further comprises a host; and the compound has a horizontal dipoleratio increased by at least 5% when compared to the exact same devicewith mCP (1,3-bis(N-carbazolyl)benzene) as host. In some embodiments,the compound has a horizontal dipole ratio increased by at least 10%when compared to the exact same device with mCP(1,3-bis(N-carbazolyl)benzene) as host.

In some embodiments of the OLED where the phosphorescent emittingcompound in the OLED has an intrinsic emission spectrum with a FWHMvalue of no more than 45 nm and an EQE of at least 25% at roomtemperature when a voltage is applied across the device, thephosphorescent emitting compound is a compound having a metalcoordination complex structure; wherein the compound is capable offunctioning as an emitter in an organic light emitting device at roomtemperature; wherein the compound has at least two ligands coordinatedto the metal; wherein the compound has a first substituent R¹ at one ofthe ligands' periphery; wherein a first distance is the distance betweenthe metal and an atom in R¹ that is the farthest away from the metal;wherein the first distance is longer than any distance between the metaland any other atoms in the compound; and wherein when a sphere having aradius r is defined whose center is the metal and the radius r is thesmallest radius that will allow the sphere to enclose all atoms in thecompound that are not part of R¹, the first distance is longer than theradius r by at least 2.9 Å.

According to another aspect of the present disclosure, a consumerproduct comprising an OLED is disclosed, wherein the OLED comprising: ananode; a cathode; and an organic layer, disposed between the anode andthe cathode, comprising a compound having a metal coordination complexstructure; wherein the compound is capable of functioning as an emitterin an organic light emitting device at room temperature; wherein thecompound has at least two ligands coordinated to the metal; wherein thecompound has a first substituent R¹ at one of the ligands' periphery;wherein a first distance is the distance between the metal and an atomin R¹ that is the farthest away from the metal; wherein the firstdistance is longer than any distance between the metal and any otheratoms in the compound; and wherein when a sphere having a radius r isdefined whose center is the metal and the radius r is the smallestradius that will allow the sphere to enclose all atoms in the compoundthat are not part of R¹, the first distance is longer than the radius rby at least 2.9 Å.

According to another aspect of the present disclosure, a consumerproduct comprising an OLED is disclosed, wherein the OLED comprising: ananode; a cathode; and an emissive layer, disposed between the anode andthe cathode, comprising a phosphorescent emitting compound; wherein thephosphorescent emitting compound has an intrinsic emission spectrum witha FWHM no more than 45 nm and an EQE of at least 25% measured at 0.1mA/cm² at room temperature when a voltage is applied across the device.

In some embodiments, the consumer products mentioned above are selectedfrom the group consisting of a flat panel display, a computer monitor, amedical monitors television, a billboard, a light for interior orexterior illumination and/or signaling, a heads-up display, a fully orpartially transparent display, a flexible display, a laser printer, atelephone, a cell phone, tablet, a phablet, a personal digital assistant(PDA), a wearable device, a laptop computer, a digital camera, acamcorder, a viewfinder, a micro-display, a 3-D display, a virtualreality or augmented reality display, a vehicle, a large area wall, atheater or stadium screen, and a sign.

EXPERIMENTAL

As previously indicated, the average transition dipole moment (TDM)alignment for a given representative EML structure can be determinedthrough angle dependent photoluminescence measurements. The angulardependence of the p-polarized emission is highly sensitive to the HDR.As such, as shown in FIG. 11, the HDR of a given emitter doped EMLsample 300 can be determined by comparing the measured p-polarizedemission e as a function of detection angle Φ to the angular dependencesimulated based on the optical properties of the sample and thecontribution of the two in-plane and one out-of-plane transition dipolemodes.

Photoluminescence measurements of Compound 152 confirm increased TDMhorizontal alignment with the substitution patterns described above. Asshown in FIG. 12, the substitution pattern of Compound 152 produces apreferentially horizontally aligned EML with HDR=0.73 as opposed to therandomly oriented nature of tris(2-phenylpyridine) iridium (HDR=0.67).

Synthesis of Compound 152

Step 1

CC-2 (2.3 g, 2.71 mmol) was dissolved in dry dichloromethane (400 ml).The mixture was degassed with N₂ and cooled to 0° C.1-Bromopyrrolidine-2,5-dione (0.81 g, 2.71 mmol) was dissolved in DCM(300 mL) and added dropwise. After addition, the temperature wasgradually raised to room temperature and stirred for 12 hrs. SaturatedNaHCO₃ (20 mL) solution was added. The organic phase was separated andcollected. The solvent was removed and the residue was coated on Celiteand purified on silica gel column eluted with toluene/heptane 70/30(v/v) to give the product CC-2-Br (0.6 g, 24%).

Step 2

CC-2-Br (0.72 g, 0.775 mmol) was dissolved in a mixture of toluene (40ml) and water (4 ml). The mixture was purged with N₂ for 10 minutes.K₃PO₄ (0.411 g, 1.937 mmol), SPhos (0.095 g, 0.232 mmol), Pd₂dba₃ (0.043g, 0.046 mmol), and phenylboronic acid (0.189 g, 1.55 mmol) were added.The mixture was heated under N₂ at 110° C. for 12 hrs. The reaction thenwas cooled down to room temperature, the product was extracted with DCM.The organic phase was separated and collected. The solvent was removedand the residue was coated on Celite and purified on silica gel columneluted with toluene/heptane 70/30 (v/v). The product was furtherpurified by recrystallization from toluene/MeOH to give Compound 152(0.7 g).

Synthesis of Compound 153

CC-2-Br-2 (0.6 g, 0.646 mmol) was dissolved in a mixture of toluene (100ml) and water (10 ml). The mixture was purged with N₂ for 10 mins. K₃PO₄(0.343 g 1.61 mmol), SPhos (0.080 g, 0.19 mmol), Pd₂dba₃ (0.035 g, 0.039mmol), and [1,1-biphenyl]4-ylboronic acid (0.256 g, 1.29 mmol) wereadded. The mixture was heated under N₂ at 110° C. for 12 hrs. Then thereaction was cooled down to room temperature, the product was extractedwith DCM and organic phase was separated. The solvent was removed andthe residue was coated on Celite and purified on silica gel columneluted with toluene/heptane 70/30 (v/v). The product was furtherpurified by recrystallization from toluene/MeOH to give Compound 153(0.64 g).

Synthesis of Compound 154

Step 1

CC-1 (2.04 g, 2.500 mmol) was dissolved in dry dichloromethane (400 ml).The mixture was degassed with N₂ and cooled to 0° C.1-bromopyrrolidine-2,5-dione (0.445 g, 2.500 mmol) was dissolved in DCM(200 mL) and dropwise added. After addition, the temperature wasgradually raised to room temperature and stirred for 16 hrs. Sat. NaHCO₃(20 mL) solution was added. The organic phase was separated andcollected. The solvent was removed and the residue was coated on Celiteand purified on silica gel column eluted by using 70/30 toluene/heptaneto give the product CC—Br (0.6 g).

Step 2

CC—Br (1.16 g, 1.296 mmol) was dissolved in a mixture of toluene (120ml) and water (12.00 ml). The mixture was purged with N₂ for 10 mins.K₃PO₄ (0.688 g, 3.24 mmol, SPhos (0.160 g, 0.389 mmol), Pd₂dba₃ (0.071g, 0.078 mmol), and phenylboronic acid (0.316 g, 2.59 mmol) was added.The mixture was heated under N₂ at 110° C. for 16 hrs. After thereaction was cooled down to room temperature, the product was extractedwith DCM. The organic phase was separated and collected. The solvent wasremoved and the residue was coated on Celite and purified on silica gelcolumn eluted by using 70/30 toluene/heptane. The product was furtherpurified by recrystallization in toluene/MeOH to give Compound 154 (1.0g).

Synthesis of Compound 155

Step 1

2-Chloro-5-methylpyridine (10.03 g, 79 mmol),(3-chloro-4-methylphenyl)boronic acid (13.4 g, 79 mmol), and potassiumcarbonate (21.74 g, 157 mmol) were dissolved in the mixture of DME (150ml) and water (20 ml) under nitrogen to give a colorless suspension.Pd(PPh₃)₄ (0.909 g, 0.786 mmol) was added to the reaction mixture, thenthe reaction mixture was degassed and heated to 95° C. for 12 hrs. Thenit was cooled down to room temperature, separated organic phase andevaporated. The residue was subjected to column chromatography on silicagel column, eluted with heptanes/THF 9/1 (v/v), providing aftercrystallization from heptanes 10 g (58% yield) of white solid.

Step 2

2-(3-Chloro-4-methylphenyl)-5-methylpyridine (10 g, 45.9 mmol),((methyl-d₃)sulfonyl)methane-d₃ (92 g, 919 mmol), and sodium2-methylpropan-2-olate (2.65 g, 27.6 mmol) were dissolved together undernitrogen to give a dark solution. The reaction mixture was heated to 80°C. under nitrogen for 12 hrs, cooled down, diluted with ethyl acetate,washed with water, dried over sodium sulfate, filtered and evaporated.Purified by column chromatography on silica gel, eluted withheptanes/THF 9/1 (v/v), providing white solid, then crystallized fromheptanes, providing colorless crystalline material (9.1 g, 81% yield).

Step 3

2-(3-Chloro-4-(methyl-d₃)phenyl)-5-(methyl-d₃)pyridine (7.45 g, 33.3mmol), phenylboronic acid (6.09 g, 49.9 mmol), potassium phosphate(15.34 g, 66.6 mmol), Pd₂(dba)₃ (0.305 g, 0.333 mmol) anddicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphane (SPhos,0.273 g, 0.666 mmol) were dissolved in the mixture of DME (150 ml) andwater (25 ml) under nitrogen to give a red suspension. The reactionmixture was degassed and heated to reflux under nitrogen. Afterovernight heating about 80% conversion was achieved. Addition of more Phboronic acid and catalyst didn't improve conversion. Purified by columnchromatography on silica gel, eluted with heptanes/THF 9/1, thenrecrystallized from heptanes to obtain white solid (6.2 g, 70% yield).

Step 4

Under nitrogen atmosphere 4,5-bis(methyl-d₃)-2-phenylpyridine (1.427 g,7.54 mmol), 5-(methyl-d₃)-2-(6-(methyl-d₃)-[1,1′-biphenyl]-3-yl)pyridine(2 g, 7.54 mmol), and [IrCl(COD)]₂ (2.53 g, 3.77 mmol) were dissolved inethoxyethanol (50 ml) under nitrogen to give a red solution. Thereaction mixture was heated to reflux for 1 hr, then precipitate wasformed. Added additional 30 mL of ethoxyethanol and reflux was continuedfor 48 hrs, then the reaction mixture was cooled down to roomtemperature. The crude material was used without additional purificationin the next step.

Step 5

Iridium dimer suspended in ethoxyethanol was mixed under nitrogenatmosphere with pentane-2,4-dione (2.59 g, 25.9 mmol) and sodiumcarbonate (3.43 g, 32.3 mmol) in 50 ml of methanol, stirred 24 hrs undernitrogen at 55° C. and evaporated. The yellow residue was subjected tocolumn chromatography on silica gel column, eluted with gradient mixtureheptanes/toluene, providing 5 g (36% yield) of the target complex.

Step 6

The acac complex (5 g, 6.72 mmol) was dissolved in DCM (20 mL), then HClin ether (16.80 ml, 33.6 mmol) was added as one portion, stirred for 10min, evaporated. The residue was triturated in methanol. The solid wasfiltered and washed with methanol and heptanes to obtain yellow solid(4.55 g, 100% yield).

Step 7

The Ir dimer (4.55 g, 3.34 mmol) and(((trifluoromethyl)sulfonyl)oxy)silver (2.062 g, 8.03 mmol) weresuspended in 50 ml of DCM/methanol 1/1 (v/v) mixture and stirred over 72hrs at room temperature, filtered through Celite and evaporated,providing yellow solid (4.75 g, 83% yield).

Step 8

The mixture of triflic salt (3 g, 3.5 mmol) and8-(4-(2,2-dimethylpropyl-1,1-d₂)pyridin-2-yl)-2-(methyl-d₃)benzofuro[2,3-b]pyridine(2.56 g, 7.7 mmol) in 30 mL of methanol were stirred under nitrogen at65° C. for 5 days. Then material was cooled down, and methanol wasevaporated. The residue was subjected to column chromatography on thesilica gel column, eluted with 2% of ethyl acetate in toluene, providingtwo isomers of the product (1.7 g with high R_(f) and 0.7 g of complexwith low R_(f)). Complex with low R_(f) is the target Compound 155.

Device Examples

All example devices were fabricated by high vacuum (<10⁻⁷ Torr) thermalevaporation. The anode electrode was 750 Å of indium tin oxide (ITO).The cathode consisted of 10 Å of Liq (8-hydroxyquinoline lithium)followed by 1,000 Å of Al. All devices were encapsulated with a glasslid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H₂Oand O₂) immediately after fabrication with a moisture getterincorporated inside the package. The organic stack of the deviceexamples consisted of sequentially, from the ITO Surface: 100 Å ofHAT-CN as the hole injection layer (HIL); 450 Å of HTM as a holetransporting layer (HTL); emissive layer (EML) with thickness 400 Å.Emissive layer containing H-host (H1): E-host (H2) in 6:4 ratio and 12weight % of green emitter. 350 Å of Liq (8-hydroxyquinoline lithium)doped with 40% of ETM as the ETL. Device structure is shown in Table 2below. Table 2 shows the schematic device structure. The chemicalstructures of the device materials are shown below.

Upon fabrication the devices have been measured for EL, JVL, andlifetime tested at DC 80 mA/cm². Device performance is shown in Table 3,voltage, LE, EQE, PE, and LT97% are all normalized to the comparativecompound.

TABLE 2 schematic device structure Layer Material Thickness [Å] AnodeITO 800 HIL HAT-CN 100 HTL HTM 450 Green EML H1:H2: example dopant 400ETL Liq:ETM 40% 350 EIL Liq 10 Cathode Al 1,000

TABLE 3 Device performance 1931 CIE λ At 10 mA/cm² at 80 mA/cm²* Emittermax FWHM Voltage LE EQE PE Lo LT_(97%) [12%] x y [nm] [nm] [rel] [rel][rel] [rel] [nits] [rel] Comparative 0.319 0.624 521 73 1.00 1.00 1.001.00 46,497 1.00 example Compound 0.315 0.628 519 71 1.02 1.04 1.03 1.0246,542 1.70 153 Compound 0.313 0.628 518 71 0.99 1.12 1.12 1.14 51,7383.00 152

Compound

Comparing Compounds 152 and 153 with the comparative example; theefficiency of both compound 152 and 153 are higher than the comparativeexample. Presumably Compound 152 and Compound 153 have higher horizontalemitting dipole orientation than comparative example. Elongated andplanar substituents with high electrostatic potential enlarge theinteracting surface region between Ir complex and host molecules;resulting in stacking Ir complexes parallel to film surface andincreasing the out coupling efficiency. Moreover, the LT_(97%) at 80mA/cm² of both Compound 152 and Compound 153 is greater than comparativeexample; indicating the elongated substituents not only increase theefficiency; but also increase the stability of the complexes in device.

Provided in Table 4 below is a summary of the device data recorded at9000 nits for device examples, the EQE value is normalized to DeviceC-2.

TABLE 4 Device ID Dopant Color EQE (rel) Device 3 Compound 154 Yellow1.24 Device C-1 CC-1 Yellow 1.10 Device C-2 CC-2 Yellow 1.00The data in Table 4 show that the device using the inventive compound asthe emitter achieves the same color but with higher efficiency incomparison with the comparative examples. It is noted that the onlydifference between the inventive compound (Compound 154) and thecomparative compound (CC-1) is that the inventive compound has a phenylmoiety replacing one of the protons in the comparative compounds, whichincreases the distance between the terminal atoms in one directionacross the Ir metal center. The device results show that the largeraspect ratio of the emitter molecule seems to be critical in achievinghigher device efficiency.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants tosubstantially alter its density of charge carriers, which will in turnalter its conductivity. The conductivity is increased by generatingcharge carriers in the matrix material, and depending on the type ofdopant, a change in the Fermi level of the semiconductor may also beachieved. Hole-transporting layer can be doped by p-type conductivitydopants and n-type conductivity dopants are used in theelectron-transporting layer.

Non-limiting examples of the conductivity dopants that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:EP01617493, EP01968131, EP2020694, EP2684932, US20050139810,US20070160905, US20090167167, US2010288362, WO006081780, WO2009003455,WO2009008277, WO2009011327, WO2014009310, US2007252140, US2015060804 andUS2012146012.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but are not limited to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, and azulene; the group consistingof aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and the group consisting of 2 to 10 cyclic structural units which aregroups of the same type or different types selected from the aromatichydrocarbon cyclic group and the aromatic heterocyclic group and arebonded to each other directly or via at least one of oxygen atom,nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom,chain structural unit and the aliphatic cyclic group. Each Ar may beunsubstituted or may be substituted by a substituent selected from thegroup consisting of deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH)or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but are notlimited to the following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40;(Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independentlyselected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and k′+k″ is the maximum number of ligands thatmay be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In anotheraspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met isselected from Ir, Pt, Os, and Zn. In a further aspect, the metal complexhas a smallest oxidation potential in solution vs. Fc⁺/Fc couple lessthan about 0.6 V.

Non-limiting examples of the HIL and HTL materials that may be used inan OLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN102702075, DE102012005215, EP01624500, EP01698613, EP01806334,EP01930964, EP01972613, EP01997799, EP02011790, EP02055700, EP02055701,EP1725079, EP2085382, EP2660300, EP650955, JP07-073529, JP2005112765,JP2007091719, JP2008021687, JP2014-009196, KR20110088898, KR20130077473,TW201139402, U.S. Ser. No. 06/517,957, US20020158242, US20030162053,US20050123751, US20060182993, US20060240279, US20070145888,US20070181874, US20070278938, US20080014464, US20080091025,US20080106190, US20080124572, US20080145707, US20080220265,US20080233434, US20080303417, US2008107919, US20090115320,US20090167161, US2009066235, US2011007385, US20110163302, US2011240968,US2011278551, US2012205642, US2013241401, US20140117329, US2014183517,U.S. Pat. Nos. 5,061,569, 5,639,914, WO05075451, WO07125714, WO08023550,WO08023759, WO2009145016, WO2010061824, WO2011075644, WO2012177006,WO2013018530, WO2013039073, WO2013087142, WO2013118812, WO2013120577,WO2013157367, WO2013175747, WO2014002873, WO2014015935, WO2014015937,WO2014030872, WO2014030921, WO2014034791, WO2014104514, WO2014157018.

EBL:

An electron blocking layer (EBL) may be used to reduce the number ofelectrons and/or excitons that leave the emissive layer. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies, and/or longer lifetime, as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the EBLmaterial has a higher LUMO (closer to the vacuum level) and/or highertriplet energy than the emitter closest to the EBL interface. In someembodiments, the EBL material has a higher LUMO (closer to the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the EBL interface. In one aspect, the compound used in EBLcontains the same molecule or the same functional groups used as one ofthe hosts described below.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. Any host material may be used with any dopant so long as thetriplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms Oand N.

In another aspect, Met is selected from Ir and Pt. In a further aspect,(Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of other organic compounds used as host are selected from thegroup consisting of aromatic hydrocarbon cyclic compounds such asbenzene, biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene,anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene,perylene, and azulene; the group consisting of aromatic heterocycliccompounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene,furan, thiophene, benzofuran, benzothiophene, benzoselenophene,carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole,imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole,dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine,triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole,indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole,quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline,naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine,phenothiazine, phenoxazine, benzofuropyridine, furodipyridine,benzothienopyridine, thienodipyridine, benzoselenophenopyridine, andselenophenodipyridine; and the group consisting of 2 to 10 cyclicstructural units which are groups of the same type or different typesselected from the aromatic hydrocarbon cyclic group and the aromaticheterocyclic group and are bonded to each other directly or via at leastone of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorusatom, boron atom, chain structural unit and the aliphatic cyclic group.Each option within each group may be unsubstituted or may be substitutedby a substituent selected from the group consisting of deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In one aspect, the host compound contains at least one of the followinggroups in the molecule:

wherein each of R¹⁰¹ to R¹⁰⁷ is independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof, and when it is aryl orheteroaryl, it has the similar definition as Ar's mentioned above. k isan integer from 0 to 20 or 1 to 20; k′″ is an integer from 0 to 20. X¹⁰¹to X¹⁰⁸ is selected from C (including CH) or N.

Z¹⁰¹ and Z¹⁰² is selected from NR¹⁰¹, O, or S.

Non-limiting examples of the host materials that may be used in an OLEDin combination with materials disclosed herein are exemplified belowtogether with references that disclose those materials: EP2034538,EP2034538 Å, EP2757608, JP2007254297, KR20100079458, KR20120088644,KR20120129733, KR20130115564, TW201329200, US20030175553, US20050238919,US20060280965, US20090017330, US20090030202, US20090167162,US20090302743, US20090309488, US20100012931, US20100084966,US20100187984, US2010187984, US2012075273, US2012126221, US2013009543,US2013105787, US2013175519, US2014001446, US20140183503, US20140225088,US2014034914, U.S. Pat. No. 7,154,114, WO2001039234, WO2004093207,WO2005014551, WO2005089025, WO2006072002, WO2006114966, WO2007063754,WO2008056746, WO2009003898, WO2009021126, WO2009063833, WO2009066778,WO2009066779, WO2009086028, WO2010056066, WO2010107244, WO2011081423,WO2011081431, WO2011086863, WO2012128298, WO2012133644, WO2012133649,WO2013024872, WO2013035275, WO2013081315, WO2013191404, WO2014142472,

Additional Emitters:

One or more additional emitter dopants may be used in conjunction withthe compound of the present disclosure. Examples of the additionalemitter dopants are not particularly limited, and any compounds may beused as long as the compounds are typically used as emitter materials.Examples of suitable emitter materials include, but are not limited to,compounds which can produce emissions via phosphorescence, fluorescence,thermally activated delayed fluorescence, i.e., TADF (also referred toas E-type delayed fluorescence), triplet-triplet annihilation, orcombinations of these processes.

Non-limiting examples of the emitter materials that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN103694277, CN1696137, EB01238981, EP01239526, EP01961743, EP1239526,EP1244155, EP1642951, EP1647554, EP1841834, EP1841834B, EP2062907,EP2730583, JP2012074444, JP2013110263, JP4478555, KR1020090133652,KR20120032054, KR20130043460, TW201332980, U.S. Ser. No. 06/699,599,U.S. Ser. No. 06/916,554, US20010019782, US20020034656, US20030068526,US20030072964, US20030138657, US20050123788, US20050244673,US2005123791, US2005260449, US20060008670, US20060065890, US20060127696,US20060134459, US20060134462, US20060202194, US20060251923,US20070034863, US20070087321, US20070103060, US20070111026,US20070190359, US20070231600, US2007034863, US2007104979, US2007104980,US2007138437, US2007224450, US2007278936, US20080020237, US20080233410,US20080261076, US20080297033, US200805851, US2008161567, US2008210930,US20090039776, US20090108737, US20090115322, US20090179555,US2009085476, US2009104472, US20100090591, US20100148663, US20100244004,US20100295032, US2010102716, US2010105902, US2010244004, US2010270916,US20110057559, US20110108822, US20110204333, US2011215710, US2011227049,US2011285275, US2012292601, US20130146848, US2013033172, US2013165653,US2013181190, US2013334521, US20140246656, US2014103305, U.S. Pat. Nos.6,303,238, 6,413,656, 6,653,654, 6,670,645, 6,687,266, 6,835,469,6,921,915, 7,279,704, 7,332,232, 7,378,162, 7,534,505, 7,675,228,7,728,137, 7,740,957, 7,759,489, 7,951,947, 8,067,099, 8,592,586,8,871,361, WO06081973, WO06121811, WO07018067, WO07108362, WO07115970,WO07115981, WO08035571, WO2002015645, WO2003040257, WO2005019373,WO2006056418, WO2008054584, WO2008078800, WO2008096609, WO2008101842,WO2009000673, WO2009050281, WO2009100991, WO2010028151, WO2010054731,WO2010086089, WO2010118029, WO2011044988, WO2011051404, WO2011107491,WO2012020327, WO2012163471, WO2013094620, WO2013107487, WO2013174471,WO2014007565, WO2014008982, WO2014023377, WO2014024131, WO2014031977,WO2014038456, WO2014112450.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies and/or longer lifetime as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the HBLmaterial has a lower HOMO (further from the vacuum level) and/or highertriplet energy than the emitter closest to the HBL interface. In someembodiments, the HBL material has a lower HOMO (further from the vacuumlevel) and/or higher triplet energy than one or more of the hostsclosest to the HBL interface.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3. ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof, when it is aryl or heteroaryl, it has the similar definition asAr's mentioned above. Ar¹ to Ar³ has the similar definition as Ar'smentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selectedfrom C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinatedto atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer valuefrom 1 to the maximum number of ligands that may be attached to themetal.

Non-limiting examples of the ETL materials that may be used in an OLEDin combination with materials disclosed herein are exemplified belowtogether with references that disclose those materials: CN103508940,EP01602648, EP01734038, EP01956007, JP2004-022334, JP2005149918,JP2005-268199, KR0117693, KR20130108183, US20040036077, US20070104977,US2007018155, US20090101870, US20090115316, US20090140637,US20090179554, US2009218940, US2010108990, US2011156017, US2011210320,US2012193612, US2012214993, US2014014925, US2014014927, US20140284580,U.S. Pat. Nos. 6,656,612, 8,415,031, WO2003060956, WO2007111263,WO2009148269, WO2010067894, WO2010072300, WO2011074770, WO2011105373,WO2013079217, WO2013145667, WO2013180376, WO2014104499, WO2014104535,

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in theperformance, which is composed of an n-doped layer and a p-doped layerfor injection of electrons and holes, respectively. Electrons and holesare supplied from the CGL and electrodes. The consumed electrons andholes in the CGL are refilled by the electrons and holes injected fromthe cathode and anode, respectively; then, the bipolar currents reach asteady state gradually. Typical CGL materials include n and pconductivity dopants used in the transport layers.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically listed substituent, such as, without limitation, methyl,phenyl, pyridyl, etc. may be undeuterated, partially deuterated, andfully deuterated versions thereof. Similarly, classes of substituentssuch as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc.also may be undeuterated, partially deuterated, and fully deuteratedversions thereof.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

We claim:
 1. A compound having a metal coordination complex structure;wherein the compound is capable of functioning as a green emitter in anorganic light emitting device at room temperature; wherein the compoundhas the formula of M(L¹)_(x)(L²)_(y)(L³)_(z); wherein L¹, L², and L³ aredifferent; wherein x is 1 or 2; wherein y is 0, 1, or 2; wherein z is 0,1, or 2; wherein at least one of y and z is not 0; wherein x+y+z is theoxidation state of the metal M; wherein when there are three ligandscoordinated to the metal, each of L¹, L², and L³ is a ligand having atleast two six-membered rings bridged together, wherein two adjacentbridged six-membered rings are each coordinated to the metal, and atleast one of the two bridged six-membered rings having at least onenitrogen atom; wherein when the metal is Pt, the compound has theformula of Pt(L¹)(L²), wherein each of L¹ and L² is a ligand, and L¹ isconnected to L²; wherein the compound has a first substituent R¹ at oneof the ligands' periphery; wherein the compound has a second substituentR² at one of the ligands' periphery; wherein R¹ and R² are on differentligands; wherein a first distance is the distance between the metal andan atom in R¹ that is the farthest away from the metal; wherein thefirst distance is longer than any distance between the metal and anyother atoms in the compound; wherein a second distance is the distancebetween the metal and an atom in R² that is the farthest away from themetal; wherein when a sphere having a radius r is defined whose centeris the metal and the radius r is the smallest radius that will allow thesphere to enclose all atoms in the compound that are not part of R¹ orR², the first distance and the second distance are longer than theradius r by at least 1.5 Å; and wherein at least one of the following istrue: the first and second distances are all longer than r by at least4.3 Å; or the compound has a transition dipole moment axis wherein anangle between the transition dipole moment axis and an axis along thefirst distance is less than 40°.
 2. The compound of claim 1, wherein thefirst and second distances are all longer than r by at least 4.3 Å. 3.The compound of claim 1, wherein R¹ is attached to an aromatic ringhaving a first coordination atom, R² is attached to an aromatic ringhaving a second coordination atom; and wherein the first coordinationatom is in a trans configuration to the second coordination atomrelative to the metal.
 4. The compound of claim 1, wherein when themetal is not Pt, the compound has a third substituent R³ at one of theligands' periphery; wherein a third distance is the distance between themetal and an atom in R³ that is the farthest away from the metal; andwherein when the radius r is the smallest radius that will allow thesphere to enclose all atoms in the compound that are not part of R¹, R²,or R³, the third distance is longer than r by at least 1.5 Å.
 5. Thecompound of claim 4, wherein R¹, R², and R³ are on different ligands;wherein the compound has an octahedral coordination geometry with threebidentate ligands, wherein each of the three bidentate ligands havingtwo coordination atoms and a midpoint defined between the twocoordination atoms; wherein the three midpoints define a first plane;and wherein each atom in R¹, R², and R³ have a point-to-plane distanceless than 5 Å relative to the first plane.
 6. The compound of claim 5,wherein any atom in R¹, R², and R³ has a point-to-plane distance lessthan r relative to the first plane.
 7. The compound of claim 1, whereinthe compound has a transition dipole moment axis; and wherein an anglebetween the transition dipole moment axis and an axis along the firstdistance is less than 40°.
 8. The compound of claim 1, wherein when themetal is not Pt, the triplet energy of a first homoleptic metal complex,whose ligands are the ligand having R¹, is lower than the triplet energyof a second homoleptic metal complex, whose ligands are any of the otherligands in the compound, by at least 0.05 eV.
 9. The compound of claim1, wherein the compound is capable of functioning as a phosphorescentemitter, a fluorescent emitter, or a delayed fluorescent emitter in anorganic light emitting device at room temperature.
 10. The compound ofclaim 1, wherein the compound comprises a first benzene ring coordinatedto the metal; and wherein the first benzene ring is fused by a secondaromatic ring.
 11. The compound of claim 1, wherein when the metal isnot Pt, L¹, L², and L³ are each independently selected from the groupconsisting of:

wherein each X¹ to X¹⁷ are independently selected from the groupconsisting of carbon and nitrogen; wherein Z¹, Z², and Z³ areindependently selected from the group consisting of carbon and nitrogen;wherein X is selected from the group consisting of BR′, NR′, PR′, O, S,Se, C═O, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″; wherein R′ and R″ areoptionally fused or joined to form a ring; wherein each R_(a), R_(b),R_(c), and R_(d) may represent from mono substitution to the possiblemaximum number of substitution, or no substitution; wherein R′, R″,R_(a), R_(b), R_(c), R_(d), R_(e) are each independently selected fromthe group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; and wherein any twoR_(a), R_(b), R_(c), and R_(d) are optionally fused or joined to form aring or form a multidentate ligand; and wherein at least one of theR_(a), R_(b), R_(c), and R_(d) includes R¹.
 12. The compound of claim11, wherein at least one pair of substituents R_(a), R_(b), R_(c), andR_(d) within the same ring are joined and fused into a ring.
 13. Thecompound of claim 11, wherein at least one pair of substituents R_(a),R_(b), R_(c), and R_(d) between two nearby rings are joined and fusedinto a ring.
 14. The compound of claim 1, wherein R¹ is selected fromthe group consisting of:


15. An organic light emitting device (OLED) comprising: an anode; acathode; and an organic layer, disposed between the anode and thecathode, comprising a compound having a metal coordination complexstructure; wherein the compound is capable of functioning as a greenemitter in an organic light emitting device at room temperature; whereinthe compound has the formula of M(L¹)_(x)(L²)_(y)(L³)_(z); wherein L¹,L², and L³ are different; wherein x is 1 or 2; wherein y is 0, 1, or 2;wherein z is 0, 1, or 2; wherein at least one of y and z is not 0;wherein x+y+z is the oxidation state of the metal M; wherein when thereare three ligands coordinated to the metal, each of L¹, L², and L³ is aligand having at least two six-membered rings bridged together, whereintwo adjacent bridged six-membered rings are each coordinated to themetal, and at least one of the two bridged six-membered rings having atleast one nitrogen atom; wherein when the metal is Pt, the compound hasthe formula of Pt(L¹)(L²), wherein each of L¹ and L² is a ligand, and L¹is connected to L²; wherein the compound has a first substituent R¹ atone of the ligands' periphery; wherein the compound has a secondsubstituent R² at one of the ligands' periphery; wherein R¹ and R² areon different ligands; wherein a first distance is the distance betweenthe metal and an atom in R¹ that is the farthest away from the metal;wherein the first distance is longer than any distance between the metaland any other atoms in the compound; wherein a second distance is thedistance between the metal and an atom in R² that is the farthest awayfrom the metal; wherein when a sphere having a radius r is defined whosecenter is the metal and the radius r is the smallest radius that willallow the sphere to enclose all atoms in the compound that are not partof R¹ or R², the first distance and the second distance are longer thanthe radius r by at least 1.5 Å; and wherein at least one of thefollowing is true: the first and second distances are all longer than rby at least 4.3 Å; or the compound has a transition dipole moment axiswherein an angle between the transition dipole moment axis and an axisalong the first distance is less than 40°.
 16. The OLED of claim 15,wherein the compound has an intrinsic emission spectrum with a FWHMvalue of no more than 45 nm; wherein the OLED has an EQE of at least 25%measured at 0.1 mA/cm² at room temperature when a voltage is appliedacross the device.
 17. A consumer product comprising the OLED of claim15.
 18. The OLED of claim 15, wherein the organic layer furthercomprises a host, wherein host comprises at least one chemical groupselected from the group consisting of triphenylene, carbazole,dibenzothiophene, dibenzofuran, dibenzoselenophene, azatriphenylene,azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, andaza-dibenzoselenophene.
 19. The compound of claim 1, wherein M is Ir.20. The compound of claim 1, wherein M is Pt.